The present invention generally relates to a tissue expander and method of using the same.
Tissue expanders are well known in the art. Traditional tissue expanders are temporarily implanted beneath skin and subcutaneous tissue of humans or animals to create a void or pocket or to stretch the skin. The implanted device is gradually inflated by injecting therein fluid or gel to force the surrounding and overlying skin to expand. Once the skin is expanded and a skin flap has formed, the device is deflated and surgically removed. A permanent, implantable device such as a mammary implant or prosthesis may be placed surgically beneath the skin flap. The expanded skin can also be excised and used in repairing a defective area in another part of the body. For detailed description of tissue expanders, see, e.g., Cohen, J. Dermatol. Sur. Oncol. 19:614-615 (1993); Hammond, et. al., Plastic and Reconstructive Surgery, 92(2):255-259 (1993); Walton and Brown, Annals of Plastic Surgery 30(2):105-110 (1993); Kenna, et al., Annals of Plastic Surgery 32:346-349 (1994). Tissue expanders have also been used in other surgery procedures. For example, tissue expanders may be implanted and inflated at a bleeding site to maintain pressure on the surface to prevent further bleeding while clotting and healing takes place. In addition, tissue expanders have also been implanted within the pelvis of patients who have had some or all of the pelvic contents removed due to cancer. In this situation, the expander excludes the small bowel from the pelvis. As a result, the small bowel which is sensitive to ionizing radiation is excluded from subsequent radiation treatment fields. See, e.g., Keno et. al., Oncology, 12(1):51-54 (1998).
In the above described applications, because the purpose is to stretch or force tissue apart or to simply fill a void, the deflation and removal of the expander generally does not significantly disrupt the surrounding areas and does not cause substantially adverse effect. Nevertheless, the removal of the expander may require an additional surgical procedure.
Tissue expanders have also been used in tissue reconstruction which involves increase of new tissue mass. For example, U.S. Pat. No. 5,716,404 to Vacanti et al. teaches applying traditional expanders in breast reconstruction involving cell transplantation. In this application, cells are injected into the area where new tissue is desired. Prior to the injection, the space for accommodating these cells is created using a tissue expander. The tissue expander is implanted in a collapsed configuration, and is then inflated by introducing therein liquid or gel. Prior to each subsequent injection of cells, the tissue expander is deflated to vacate a space equivalent to the volume of the cell suspension to be injected. Once the space is filled with cell suspension or new tissue, the tissue expander is surgically removed using anesthetic incisions.
In reconstructive applications, removal of the expander could be potentially problematic as new tissue grows and surrounds the slowly deflating expander. The retrieval of such a device may disrupt newly developed tissue and become counterproductive. On the other hand, in traditional expander applications as fillers or expanders, disruption of new tissue usually is not a concern. Yet, removing the expander may require complex surgical procedures.
The absorbable tissue expander device of this invention successfully solves these problems. It would maintain mechanical integrity for a desired period of time and would gradually absorb to complete loss of mass, thus requiring no removal procedure.
Accordingly, an absorbable tissue expander and methods of using the device are provided in accordance with the present invention. The bioabsorbable tissue expander comprises a fluid-tight envelope and means for the controlled inflation and deflation of said envelope after the device is implanted in a tissue. The envelope has a bioabsorbable biocompatible shell defining a chamber. The envelope is inflatable upon infusion of fluid into the chamber and is deflatable upon withdrawal of fluid from the chamber or by release of fluid into the surrounding area through the shell as a result of biodegradation. Examples of suitable bio-absorbable materials for making the shell include but are not limited to polyesters, polyanhydrides, polyurethanes, polyphosphazenes, polyorthoesters, polyoxalates, polycaprolactone, copolymers of lactide and ecaprolactone, polyetheresters, polycarbonates, polyamides, polyacetals, polycyanoacrylates, polyethylene oxide, and elastomeric polypeptides.
The inflation and deflation means may include any conventional designs known in the art, e.g., injection ports having a hollow region which is in fluid communication with the interior of a chamber, or a self-sealing means comprising injecting or removing fluid from the chamber with a needle penetrating through the shell and self-sealing of the shell by the flowing together of shell wall material at the needle hole. Additionally, the deflation may be caused by the release of fluid across the shell wall of the expander as a result of the gradual biodegradation of the shell wall. The fluid used typically is liquid or gel, e.g. saline liquid. Materials for modifying cell growth such as growth factors may also be included in the envelope, either associated with the shell wall or simply mixed in the fluid or gel.
In a preferred embodiment, the absorbable tissue expander of the present invention has a plurality of fluid-tight envelopes. Each envelope has a chamber defined by a bio-absorbable biocompatible shell. Each envelope also has a separate means for controlled inflation and deflation of the envelope after the device is implanted in a tissue. In addition, each envelope is processed to have unique mechanical properties and mass loss profile. Therefore, it is possible to allow sequential deflation of the envelopes and sequential absorption of the shell material.
The present invention further provides a method of reconstructing a tissue using the absorbable tissue expander of the present invention. In the method, the device is implanted in the tissue to be reconstructed and the envelope(s) is inflated with biocompatible liquid or gel to create a space for the growth of new tissue. As the tissue surrounding the envelopes grows, the envelopes are gradually deflated or degraded so as to provide space for further tissue development until the envelopes are completely deflated and gradually absorbed by the developed tissue.
In accordance with another embodiment of the present invention, a method of adjusting the position of an organ or tissue inside the body of a living subject is provided. An absorbable tissue expander of the present invention is implanted in proximity to the organ or tissue and is thereafter inflated to contact or dislocate the organ or tissue. In a preferred embodiment, the method is used to exclude the small bowel from a radiation treatment field. The absorbable tissue expander is preferably deflated by means of biodegradation of the expander material while allowing for its fluid contents to disseminate into the surrounding body cavity.
Absorbable expanders can also be designed to release a wide variety of biologicals over time including cytokines, growth factors, antineoplastic, chemotherapy agents, adhesion preventing agents and the like.
The foregoing and other advantages and features of the invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying examples, which illustrate preferred and exemplary embodiments.